Liquid crystal displays are commonly used as displays for compact electronic apparatuses. This is because they not only provide good quality images with little power consumption, but also because they are very thin. The liquid crystal in a liquid crystal display does not emit any light itself. The liquid crystal has to be lit by a light source so as to clearly and sharply display text and images. Thus, a backlight module is generally needed for a liquid crystal display.
Referring to FIG. 4, a conventional LCD 100 includes an LCD panel 11, and a backlight module 12 at one side of the LCD panel 11. The backlight module 12 provides a planar light source to illuminate the LCD panel 11.
The LCD panel 11 includes a first polarizer 13, a first substrate 14, a liquid crystal layer 141, a second substrate 15, a second polarizer 16, a flexible printed circuit (FPC) 151, and a printed circuit board (PCB) 152. The first substrate 14 and the second substrate 15 are disposed parallel to each other, and are spaced apart a predetermined distance. The liquid crystal layer 141 is interposed between the first substrate 14 and the second substrate 15. The first polarizer 13 is disposed on an outer surface of the first substrate 14, and the second polarizer 16 is disposed on an outer surface of the second substrate 15. One terminal of the FPC 151 is connected to the PCB 152, and another terminal of the FPC 151 is disposed on an edge portion of the second substrate 15. The second substrate 15 includes a plurality of driver circuits (not shown). The driver circuits are electrically connected to the FPC 151.
The backlight module 12 includes a set of optical films 17, a light guide plate (LGP) 18, a light source 19, and a reflective film 190. The LGP 18 has a generally rectangular shape, and includes a light incident surface 181, a light emitting surface 182 adjoining the light incident surface 181, and a bottom surface 185 adjoining the light incident surface 181. The light source 19 is disposed adjacent to the light incident surface 181 of the LGP 18. The set of optical films 17 is disposed adjacent to the light emitting surface 182 of the LGP 18. The reflective film 190 is disposed adjacent to the bottom surface 185 of the LGP 18. The light source 19 can be a linear light source.
In operation, light beams emitting from the light source 19 enter the LGP 18 through the light incident surface 181 thereof. Some of the light beams subsequently exit the light emitting surface 182 of the LGP 18, pass through the set of optical films 17, and finally reach the LCD panel 11. Other of the light beams subsequently exit the bottom surface 182 of the LGP 18, are reflected by the reflective film 190 back into the LGP 18, exit the light emitting surface 182 of the LGP 18, pass through the set of optical films 17, and finally reach the LCD panel 11. In this way, the backlight module 12 effectively changes the linear light source 19 into a surface light source, which evenly illuminates a whole display screen area of the LCD panel 11.
With innovations in science and technology, the LGP 18 is capable of being made very thin; for example, in the range from 0.7 mm to 0.45 mm. However, light source technology has not kept up with advances in LGP technology. Generally, a corresponding minimum thickness of the light source 19 is about 0.6 mm. Therefore it is common for the light source 19 to be thicker than the LGP 18. In such case, an area of the light incident surface 181 is less than a light emitting area of the light source 19. Thus, the efficiency of utilization of light energy of the light source 19 may be unsatisfactory.
What is needed, therefore, is an LCD that can overcome the above-described deficiencies.